At present, future worldwide phosphorus resources exhaustion is predicted, and from the domestic conditions that securement of phosphorus resources is dependent on importation, attention is paid to the technique for recovering phosphorus contained in the wastewater.
Heretofore, as for phosphorus in the wastewater, discharge of phosphorus into the environment system is a factor of eutrophication, hence removal of phosphorus and discharge state management thereof have been regarded as indispensable, and thus efforts have been concentrated mostly on the phosphorus removing technique. As representative phosphorus removing techniques, there are the biological phosphorus removing method utilizing phosphorus-accumulation capability of microorganism, and phosphorus removing method based on the coagulating sedimentation.
In order to use these phosphorus removing methods as direct phosphorus recovery/utilization means, for example, processes of incineration, chemical treatment, and the like of excess sludge resulting from the biological phosphorus removing method have been required, and it has been necessary to use a large amount of chemical agents, and arrange a plurality of treatment processes. For example, in order to reuse the phosphorus as resources, it is also necessary to eliminate influences of the used chemical agents and impurities contained in the derived sludge, and hence adjustment and refinement processes of the phosphorus also become necessary. In view of these circumstances, attention is paid to a water treatment technique utilizing a phosphorus adsorbent configured to selectively adsorb phosphorus. Examples of a material used to selectively remove an anion include a phosphorus adsorbent in which an anion-exchange resin or hydrotalcite-like inorganic layered compound is basically used as an anion exchanger, and adsorbent in which various metals are basically used as an anion exchanger. Regarding methods of manufacturing these adsorbents, a phosphorus adsorbent formed by developing the material characteristics of the above adsorbents, and phosphorus recovery utilizing the phosphorus adsorbent, a large number of methods are proposed.
As an example of a phosphorus recovery system utilizing these adsorbents, there is a system disclosed in JP-A 2008-264661 (KOKAI).
In JP-A 2008-264661 (KOKAI), a method is described in which in order to prevent the consumption of the chemical agent serving as the water passing liquid from increasing, the wastewater to be treated is made to flow through a reaction vessel filled with a phosphorus adsorbent, thereafter a chemical agent is poured into the vessel for a while, and thereafter the adsorbent is immersed in the stationary chemical agent, whereby the phosphorus that has been adsorbed is desorbed, and a liquid remaining in the container is discharged in advance by supplying a gaseous body into the container before passing the chemical agent and the like.
However, in the wastewater treatment described in JP-A 2008-264661 (KOKAI), there is the possibility of the amount of the passed liquid being prevented from increasing, whereas there is the possibility of the desorption being not completely advanced between the adsorbent and chemical agent containing phosphorus concomitantly with an increase in the concentration of the phosphorus desorbed from the adsorbent by the immersion of the adsorbent in the desorption chemical agent. Accordingly, by the method disclosed in JP-A 2008-264661 (KOKAI), when the adsorption operation is repetitively carried out, a sufficient actual adsorption capacity cannot be obtained in spite of the adsorption capacity originally possessed by the phosphorus adsorbent. As a result of this, there are the problem of an increase in the used amount of the adsorbent, and problem that upsizing of the equipment is brought about. Further, there is the problem that when the liquid is reintroduced into the adsorbent by discharging the liquid from the reaction container of the adsorbent by the introduction of the gaseous body, the gaseous body remains in the container, and contact of the liquid to be introduced in the subsequent process with the adsorbent is obstructed by the remaining gaseous body, whereby lowering of the efficiency of adsorption of phosphorus by the introduction of the wastewater to be treated, and efficiency of discharge of the phosphorus by the introduction of the chemical agent is caused.
Further, as another problem, there is the problem that in the phosphorus removal of the wastewater containing phosphorus, when an alkaline liquid serving as a chemical agent liquid for desorbing the phosphorus captured by the phosphorus adsorbent is made to flow in a circulating manner, there is the possibility of the desorption being not completely advanced between the phosphorus adsorbent and chemical agent liquid containing phosphorus concomitantly with an increase in the concentration of the phosphorus in the chemical agent liquid, and hence when the adsorption operation is repetitively carried out, a sufficient actual adsorption capacity cannot be obtained in spite of the adsorption capacity originally possessed by the phosphorus adsorbent, and consequently, the used amount of the adsorbent is increased, and upsizing of the equipment is caused.
At this time, regarding the impurities contained in the wastewater to be treated containing phosphorus, after the phosphorus is adsorbed and removed, the alkaline liquid for desorbing the phosphor is passed through the wastewater, thus the impurities contained in the wastewater to be treated are mixed into the alkaline liquid for desorbing the phosphorus in addition to the phosphorus desorbed by the alkaline liquid and moved to the alkaline liquid which has been passed through the wastewater, and hence there is the problem that the impurities are mixed into the phosphorus recovery liquid.
Embodiments have been contrived to solve the problems described above, and an object thereof is to provide a water treatment equipment configured to recover phosphorus, in which the sludge-separated liquid discharged from a treatment process of sludge discharged from a biological water treatment process is made the water to be treated, phosphorus contained in the water to be treated is separated from the water by using an adsorbent, and which is capable of efficiently carrying out an operation of bringing the water to be treated with an agent liquid while preventing the impurities in the water to be treated from being mixed into the recovered phosphorus.
In general, according to one embodiment, a water treatment equipment comprises a phosphorus adsorbent which adsorbs phosphorus contained in water to be treated; a reactor vessel filled with the phosphorus adsorbent; an introduction path configured to introduce the water into the reactor vessel, and a discharge path configured to discharge, from the reactor vessel, the water from which phosphorus has been removed; a first liquid passing mechanism configured to pass, through the reactor vessel, a phosphorus desorption agent liquid which desorbs phosphorus from the phosphorus adsorbent which has adsorbed phosphorus; a phosphorus recovery mechanism configured to recover phosphate from the phosphorus desorption agent liquid which has been subjected to the passing treatment; a second liquid passing mechanism configured to pass and circulate, through the reactor vessel, a regeneration agent liquid which generates the phosphorus adsorbent; and a discharge mechanism configured to discharge the liquid held in the reactor vessel after passing the water or the phosphorus desorption agent liquid through the reactor vessel.